Concentration of dilute sulphuric acid containing amyloid



Patented Feb. 2, 1937 UNITED STATES PATENT OFFICE CONCENTRATION OF 'DILUTE SULPHURIC erson Parchment Township, Pa.

Paper Company,

Bristol No Drawing. Application April 17, 1935, Serial No. 16,891

'5 Claims.

The present invention :relates to concentration of sulphuric acid initially containing carbonizable organic matter, and more particularly to sulphuric acid which has been used for the parchmentizing of paper or waterleaf.

Whereas, my invention can be applied to sulphuric acid containing many kinds of organic matter, which can, by the application of heat be decomposed and carbonized, the invention will be described here as it relates to the recovery of strong sulphuric acid from parchmentizing processes.

In making vegetable parchment the waterleaf paper is passed through a bath of cold sulphuric acid (for example sulphuric acid of about 68 to 73% strength, and preferably between 70% and 71% strength) at temperatures of about 50 to 60 F. The sheet being treated may conveniently be a 23 pound paper or a 25 pound paper, and preferably a paper which is somewhat porous. The parchmentized'paper is then washed with cold water or with cold dilute acid and then with cold water, preferably counter-current, until the paper is substantially free from free acid, after which the paper is dried and subsequently rolled up or cut into sheets of the desired size. The dilute sulphuric acid, forming a byproduct is, in some plants, reconcentrated for reuse in the parchmentizing process.

During the process of parchmentizing paper or waterleaf some of the surface fibres of the paper are, by the action of the machinery and acid, removed from the surface of the paper into the sulphuric acid of the parchmentizing bath or into the washing bath, and these fibres having been parchmentized with the paper from which they are detached, constitute what is known in the art as fuzz or amyloid, and heretofore, during the concentration of the sulphuric acid, this amyloid or fuzz together with any organic matter dissolved by the acid, was wholly or partially decomposed, which blackened the acid, rendering it unsuitable for parchmentizing further amounts of paper, if the best results are desired. This black color therefore had to be removed. This material amyloid referred to consists of cellulose and/0r carbonizable decomposition products of cellulose. The term carbonizable carbohydrate material derived from paper will be used in certain of the claims to cover said substances, whatever may be their exact chemical composition.

The process as described and claimed in Patent 1,836,849, Arthur Hough, has heretofore been employed satisfactorily for bleaching the sulphuric acid after carbonization of the organic material therein, which will hereinafter be re.- ferred to as amyloid.

In the present invention, the novelty consists in first oxidizing the said organic matter into materials which are uncarbonizable by heating in the presence of sulphuric acid. In this way it is readily possible to prevent the carbonization, of said organic material, and to prevent the blackening of the acid containing the organic material, and still concentrate the acid up to the strength required for parchmentizing or similar operations, in which the said acid is to be used.

Various kinds of oxidizing agents can be employed for accomplishing this oxidation, nitric acid being generally satisfactory, as well as nitrate. Ammonium nitrate is suitable, also hydrogen peroxide or a solution of the same. The present invention is not limited to the use of particular oxidizing agents. Nitric acid seems thus far to be the most suitable oxidizing agent to use. Permanganates, chromates and the like can be employed, but these are somewhat less suitable because the chromium or manganese left in the final acid is undesirable in the parchmentizing process. Nitric "acid is now believed to be the most satisfactory oxidizing agent, and only a very small amount of this is necessary, the amount of course depending upon the amount of organic matter in the sulphuric acid under treatment; With the amount of amyloid which is ordinarily present in a 20 or 25% sulphuric acid obtained by washing the waterleaf, as little as 0.01% of nitric acid, based on the amount of dilute sulphuric acid is sometimes sufficient.

The oxidizing agent, say nitric acid, is added to the dilute sulphuric acid, and the temperature raised to about or preferably C., and the mass is preferably kept at this temperature for a short time, say one or two hours, during which period the amyloid will become oxidized, probably being converted largely into oxalic acid. The oxidation products of the amyloid are noncar bonizable, and when the dilute sulphuric acid then goes into the concentrators, the oxalic acid, or other oxidation products of the amyloid will be broken up into carbon dioxide, carbon monoxide and water, and they do not blacken the acid. The acid is concentrated in any desired manner, up to the strength required. If a small excess of nitric acid is added, above the amount necessary for the oxidation of the amyloid, this small excess Will be removed during the concentration of the sulphuric acid. During the concentration of the sulphuric acid, it is advisable to bubble air through the said acid being concentrated, which assists in carrying 01f the nitric acid.

In a particular run of the process, each 1000 lbs. of dilute sulphuric acid coming from the countercurrent Washer used in washing parchmentized paper, contained 450 lbs. (or 45%) of actual H2804 and .289 1b. of organic matter, 1.43 lbs. of nitric acid of concentration was added to each 1000 lbs. of the said dilute sulphuric acid. This amount of nitric acid is about five times the amount of amyloid in the dilute sulphuric acid. The process was conducted as above described. After concentration to 70%, the acid was substantially light amber color and after cooling was entirely suitable for reuse in parchmentizing paper.

The above figures indicate that it takes approximately .l% HNO3 nitric acid (figured as I-INOs of to produce the required finished color of the acid. In other Words, for every 1000 lbs. of weak acid it would require approximately 1 lb. of 100% HNOz to produce the oxidation of the amyloid and any other organic matter present, into uncarbonizable organic substances. These figures apply only to acid having the stated content of carbonizable organic matter.

When acid of the same strength with half the above amount of amyloid present is to be concentrated, it requires approximately one-half of the above stated amount of nitric acid to produce the same color in the concentrated acid.

I claim:

1. A process of treating a weak sulphuric acid solution containing carbonizable carbohydrate material derived from paper, in an uncarbonized condition, which comprises adding to said solution, without carbonization of said carbohydrate material, an oxidizing agent for said carbohydrate material to give a non-carbonizable material, and thereafter heating and concentrating said acid, whereby a concentrated acid is produced which does not contain black carbonization products of said carbohydrate material.

2. A process of treating a weak sulphuric acid solution containing carbonizable carbohydrate material derived from paper, in an uncarbonized condition which comprises adding to said solution, without carbonization of said carbohydrate material, an agent selected from the herein described group consisting of nitrogen-oxygen-containing acids and salts thereof, in amount sufficient to oxidize the said carbohydrate material to a noncarbonizable substance, and thereafter heating suificiently to convert the carbohydrate material into non-carbonizable material, concentrating said acid, whereby a concentrated acid is produced which does not contain black carbonization products.

3. A process of destroying carbonizable carbohydrate material derived from paper and similar carbonizable organic matter in dilute sulphuric acid resulting from the washing of cellulosic materials after a sulphuric acid treatment, which comprises adding a substance containing the nitric acid radical to such dilute acid containing such organic constituents in an uncarbonized condition, to oxidize said uncarbonized organic constituents into an uncarbonizable compound, and thereafter heating and concentrating said acid.

4. A process of producing parchmentizing acid, from the washings of sulphuric-acid-parchmentized paper, which washings contain Water, sulphuric acid and carbonizable organic material derived from the paper being parchmentized, which process comprises adding to said washings, before carbonization of any considerable amount of the said carbonizable organic material has occurred, a small amount of an oxidizing agent which contains combined nitrogen and oxygen, maintaining the washings and said oxidizing agent at a temperature high enough to convert the said carbonizable organic material into noncarbonizable substances, and thereafter concentrating the acid washings to parchmentizing strength, without blackening the same by carbcnization.

5. A process of producing parchmentizing acid, from the washings of sulphuric-acid-parchmentized paper, which washings contain water, sulphuric acid and carbonizable organic matter derived from the paper being parchmentized, which process comprises adding to said washings, before carbonization of any considerable amount of the carbonizable organic matter has occurred, nitric acid equal to about five times the amount of the carbonizable organic matter in said washings, heating the mixture only to about IOU- C., until the carbonizable organic matter has been substantially completely converted into uncarbonizable substances which are readily decomposable during concentration of the acid to parchmentizing strength, and thereafter concentrating the acid washings to parchmentizing strength, without blackening the same by carbonization.

JOHN ROY DUFFORD. 

